Trans-dimethylcyclohexanedicarboxylate (trans-DMCD) is useful for the synthesis of polyesters having enhanced weatherability as well as other unique properties. DMCD is commercially produced as a mixture of cis and trans isomers from the hydrogenation of dimethylterephthalate, with the major isomer being the cis configuration. In order to obtain useful quantities of trans-DMCD, the mixture is treated with a catalyst to isomerize the mixture to the thermodynamic equilibrium of 65% trans and 35% cis.
It is known that this isomerization can be carried out with a homogeneous catalyst comprised of the half acid ester of DMCD as the catalyst. The disadvantages of this approach are that long reaction times (48 h) are generally required and the yield of trans-DMCD is typically low (i.e., 70%-80%)--thus providing economic drawbacks as well as the adverse consequences of large amounts of wasteful by-products.
Traditional methods of isomerization such as treatment of the ester with a strong base such as methoxide are not generally considered acceptable in a large scale industrial process because of the expense associated with separating the base from the product mixture.